The invention relates to a wireless network comprising at least a base station and a plurality of assigned terminals for exchanging user data and control data.
In the document xe2x80x9cETSI SMG2, Meeting no. 24, Cork, Ireland, Dec. 1-5 1997, Tdoc SMG2 359/97, Concept Group Alphaxe2x80x94Wideband Direct-Sequence CDMA (WCDMA), EVALUATION DOCUMENT (3.0), part 1: System Description, Performance Evaluationxe2x80x9d a radio network operating according to the CDMA method (CDMA=code-division multiple access) is proposed. The radio network comprises a plurality of radio cells having each a base station and terminals or mobile stations located therein. After a terminal has been registered and synchronized, it sends a random-access burst over a random-access channel RACH, for example, when a user channel is requested. The random-access burst comprises a preamble part and a data part. The preamble part comprises 16 orthogonal symbols (preamble sequence) which is spread by a Gold code (preamble code). The Gold code contains 256 chip intervals. The data part contains a field with an identification for the terminal, a field for featuring the requested service (short packet transmission, dedicated-channel set-up, etc.), an optional field for data packets (optional user packet) and a CRC field for error detection. A random-access burst received from a base station is supplied via a matched filter, a preamble correlator, a peak detector to a circuit portion estimating the time delay of the data part, which circuit portion controls a rake circuit for the evaluation of the data part. Thus, a peak detection based on a correlation is used here with subsequent message decoding. To the terminals assigned to a base station there are 80 random-access channels available. These channels are determined by 16 different preamble codes and 5 different transmission instants. If two or more terminals transmit over the same random-access channel i.e. the same preamble code and transmit time is selected, there will be a collision and the information transmitted by the terminals cannot be correctly evaluated by the base station. Such collisions are especially probable with heavy traffic loads.
It is an object of the invention to provide a wireless network in which a terminal exchanges signaling information with the assigned base station in a different manner.
With a wireless network of the type defined in the opening paragraph, the object is achieved in that the base station is provided for transmitting the start time of at least one signaling sequence of at least one terminal, in that the base station includes a device for correlating a received signaling sequence and for detecting the pulse evolved from a received and correlated signaling sequence and in that the base station, after receiving a signaling sequence, is provided for rejecting or acknowledging the request for channel capacity from a terminal over a channel collectively used by a plurality of terminals.
The wireless network according to the invention is understood to mean a network comprising a plurality of radio cells in which a respective base station and a plurality of terminals transmit control data and user data in a wireless fashion. A wireless transmission is used for transmitting information, for example, by radio, ultrasonic or infrared channels.
After the registration and synchronization, a terminal is to request a certain user channel from the assigned base station for transmitting user data. Such a user channel may be, for example, a dedicated user channel (for example, for speech transmission) either between base station and terminal or between two terminals. The channel assignment is carried out by the base station. According to the invention a terminal sends a request, for example, for a dedicated user channel through a signaling channel predefined by the base station. The base station is to announce to the terminals at least the start time of a signaling sequence that may be known beforehand. Alternatively, it is possible that, in addition to the start time also one of various signaling sequences is assigned to the terminals. Such a signaling sequence is a Gold or a Casami sequence having good auto and cross-correlation properties. The base station includes a device (for example, a matched filter) in which a correlation is effected of the received signaling sequences. The pulse evolved from the correlation is detected and assigned to a terminal. Since a collision in the network according to the invention is avoided as a result of different start times of the signaling sequences, and no message decoding is executed after a peak detection based on a correlation, but the appearance of the pulse evolved from the signaling sequence is considered a signaling request, a signaling detection especially with heavy traffic loads can be executed in a more robust and faster way than in the state of the art.
For detecting a signaling sequence, a certain time range is selected for the peak detection, which range depends on the start time of the signaling sequence and on the channel properties. Such a time range is denoted as a detection window. The length or duration and the start time of the detection window is to be selected such that a peak detection is possible. The detection windows are shorter than the time duration of the random-access bursts known from the state of the art. By means of the signaling according to the invention, many terminals can thus send a signaling request within a short period of time.
After the registration and synchronization, a terminal in a radio cell has always the same start time relative to a reference frame for transmitting a signaling sequence, as long as the base station does not explicitly change this start time. Thus one signaling channel is permanently occupied for one terminal. Since many start times may occur within the reference frame which is of short duration (for example, 10 ms) and since all the terminals of a radio cell use the same signaling sequence, only few network resources are used when a terminal is permanently assigned a start time and a signaling sequence.
The signaling sequences of all the terminals in a radio cell have different start times. In the simplest case, each terminal uses the same signaling sequences. The signaling sequences may therefore partly overlap, because the length of a sequence is usually longer than the distance between two successive start times.
An advantage of the network according to the invention also comprises the certainty with which a signaling request is recognized. Practically always after the transmission of a signaling sequence, a detectable pulse is generated. This is caused by the fact that interference signals and channel noise may lead to xe2x80x9cartificialxe2x80x9d pulses on the output of the matched filter. It is highly unlikely for these artificial pulses to reduce the amplitude of the pulses on the output of the matched filter when an actually transmitted signaling sequence has been received. In the worst case (for example, in the event of interference) a false alarm is made when the amplitude of the interference or noise signal surpasses the detection threshold without a signaling sequence having been sent.
The signaling sequence may also be used for requesting channel capacity of a shared uplink channel. The base station, after receiving a signaling sequence, either rejects the request or acknowledges the request for channel capacity from the terminal over a channel which is shared by a plurality of terminals. The use of a shared channel provides a capacity increase because of static effects.
The acknowledgement or rejection of the channel capacity for at least one terminal is sent by the base station to the respective terminal via an access control channel. By means of the acknowledgement, the base station sends further information which relates to the transmission of user data over the shared channel. Such information may relate to the start time of the transmission of the user data, data rate, the transmission power, the spreading factor and so on.
The shared channel may be used by, for example, 8 terminals for transmitting user data. If a further terminal wishes to use this channel, this terminal will transmit a further specific signaling sequence. The base station tests whether the terminal can be included in the group of various of terminals using the shared channel. If the result of the test is positive, the base station announces to the respective terminal that it is included in the group.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.